Power and Energy

What is the difference between Power and Energy?

To determine what solar system will meet your needs you will need to know how much power you will use at any point in time and how much energy you consume on a regular basis. Power and energy are sometimes confused.


An electrical load (e.g. a lamp, kettle, hairdryer, etc.) has a rated "size" in watts. This is the POWER level and is the instantaneous rate at which energy is consumed to run the appliance/device. How much ENERGY is consumed at that rate depends on how long the device is running. Usually the power level remains constant while the appliance or device is running however the amount of energy used increases over time. Both power and energy are important components to consider as the solar power system you choose for your RV or marine vessel must be able to cater for:

  • Your power needs (how many appliances/devices you are using at any one point in time). In other words the energy you are drawing down at once
  • Your energy needs (how long you use the appliance in a day. In other words how much energy are you using up each day which would drain your battery reserve.

A watt (W) is a measure of how much electrical energy is being used. One watt of electrical power, maintained for one hour, equals one watt-hour of energy.  A Watt hour (Wh) therefore represent the estimated amount of energy an electrical appliance consumes in one hour.

1000W equals one kilowatt (kW).   One watt for a thousand hours or a thousand watts for one hour both the same amount of energy and equals one kWh. 


When we are calculating what size solar power system to install in a caravan/RV we consider how many watts your appliances use and how long you use them for.


How do you work out the watt hours (Wh) for appliances/devices?  

Link to how to calculate watt hours

See our list of watts for common applicance and how to calculate the watt hours: